This invention relates to the assessment of safe vehicular speeds, and more particularly to measuring populations of drivers in varying driving conditions to determine such safe speeds. In some aspects, a goal is to determine a “customized speed limit” based on the individual driver and the road conditions at the time of travel.
Drivers, municipalities and insurance companies have a shared interest in encouraging people to travel at safe speeds. Determining a safe speed, however, can be difficult.
Frequently, safe speeds have been determined by comparison with an official speed limit. Municipalities typically set speed limits by performing a “traffic and engineering survey”. The survey measures actual driving speeds on the road in question and the speed limit is often set based on the 85th percentile of observed speed. The decision to use the 85th percentile was motivated by the “Solomon Curve” shown in FIG. 1. This curve shows that the risk of crash is related to the deviation from the average speed; traveling significantly faster or slower than the typical speed is associated with an elevated rate of crashing.
A single official speed limit, however, presumes that there is a universal safe speed for a road segment. However, a safe speed is highly dependent on the driver and the road conditions. For example, the speed limit may not reflect a safe speed because of weather (rain, snow, fog, wind speed), construction, darkness, sun glare, traffic, an inexperienced driver, an exhausted driver, or a host of other factors.
Furthermore, it can be difficult to gauge the degree of safety based solely on a single speed limit. For example, exceeding the speed limit by 15 miles per hour may be safe on some roads but dangerous on others. Because of this ambiguity, there is no accepted method to compare a driver's fine-grained speeding behavior across different road segments. Therefore, it can be difficult to identify where a driver's most dangerous speeding occurs.
This difficulty makes it harder to help drivers modify their own behavior to become safer, and harder for municipalities or insurance companies to assess risk.